1. Field of the Invention
The present invention relates in general to continuously variable traction roller transmissions, and more particularly to the transmissions of a double cavity type which has on a common axis two sets of motion transmitting traction mechanisms.
2. Description of the Prior Art
Japanese Patent First Provisional Publication 61116166 shows one continuously variable traction roller transmission having motion transmitting traction rollers disposed between, and in engagement with, opposite toroidal discs mounted on input and output shafts. Under operation of the transmission, the torque applied to the input toroidal disc from a prime mover is transmitted through the traction rollers to the output toroidal disc.
During this, the rotation speed change ratio between the input and output toroidal discs is infinitely varied depending on the angle at which each traction roller inclines relative to the common axis on which the input and output toroidal discs are mounted.
In order to avoid slippage between each traction roller and the input and output toroidal discs, a biasing device is employed by which the mutually engaging roller and disc are biased toward each other. The biasing device is controlled by a controller in such a manner that the biasing force is varied in proportion to a torque applied to the input toroidal disc. Usually, a disc spring is used for the biasing device, and loading cams are used for the controller.
Thus, when a large torque transmitting is required, it becomes necessary to provide the transmission with a stronger and thus large-sized biasing device. In this case, however, the entire construction of the transmission becomes large in size, particularly, in the size in radial direction.
In order to solve this drawback, there has been proposed a so-called double cavity type transmission which has on a common axis two sets of motion transmitting traction mechanisms. This type of transmission is shown in the Publication entitled "Machine Design" published on Apr. 18, 1974 and SAE (Society of Automotive Engineers, Inc.) Paper 751180. That is, by bearing the input torque by the two motion transmitting traction mechanisms, each mechanism is allowed to have a small size particularly in radial direction thereby permitting reduction in radial size of the entire construction of the transmission. As is known, reduction in size of automotive parts is quite advantageous in the manufacturing of motor vehicles.
In fact, in the transmission of such type, the input and output shafts are arranged in parallel and the two sets of motion transmitting traction mechanisms are arranged at the output shaft side. The input and output shafts extend throughout the entire internal length of the casing of the transmission.
However, due to the inherency of the above-mentioned arrangement of the input and output shafts, it is difficult to provide the interior of the casing with a sufficient space for accommodating any parts. Thus, hitherto, a control valve used for controlling the motion transmitting traction mechanisms has been mounted outside of the transmission casing. Thus, in spite of employing the double cavity structure, the attempt to reduce the size of the transmission has been far from satisfactory.